One absentminded ancient philosopher forgot to wind up his only clock in the house.
He had no radio, TV, telephone, internet, or any other means for telling time.
So he traveled on foot to his friend’s place few miles down the straight desert road.
He stayed at his friend’s house for the night and when he came back home,
he knew how to set his clock. How did he know?

before he left his house he wound up his clock. so he knew the total amount of time he was gone. at his friends house using his friends clock he noted the time he arrived there and when he left. he then subracted the amount of time spent at his friends house from the total amount of time away from his hous giving him his total waling time. divided that by 2 gave him the average one one trip. added that to the time that he left his friends house and that would be the time he arrived back at his house

When he leaves his friend's house, he looks at his friend's clock, then he starts walking back home, doing 1 second long steps. Every 60 steps he adds a minute to the time he remembered. When he's back home he knows what time it is and can set his clock.

He could have recieved any kind of time keeping device from his friend like an hour glass or simply a watch. Remembering the time of his friend's clock and the time passed since his visit would give him the correct time to set at home.

he winds up his clock and notes the exact time on his clockthen he immediately starts walking to his friends placehe notes the exact time on his friend's clock when he arrives and stays for the night and starts back exactly 24 hrs after he first arrived and notes the time before leavinghe walks back and quickly notes the time on his clock and exactly finds out the time period for which he had left after winding his clock.he subtracts 24 hours from this time period and adds the remaining to the time that he had noted in his friends place before he left and sets his clock to that time.

"He stayed at his friend’s house for the night."He remembers what time sunrise/sunset is on his friend's clock and sets his own clock the following night. In Greece (assuming that's where he's from) sunrise changes by 2 mins per day so he can add those additional 2 mins. He now knows that his clock is correct to within two minutes.

He could know how to set his clock by determining his average walking speed and the distance to his friend's house so that he knows the amount of time that it takes to get from one house to the other. That way, if he knew how long it took him to get home, he could have looked at the clock at his friends house (if his friend had a clock...it does not explicitly say that but I'm assuming...otherwise he has learned to tell time from the sun or is setting the clock to a random time, since it does not state that he sets the clock correctly) and added the time spent traveling home to the time shown on his friends clock. That way his clock would be correct.

Suppose philosopher started from his home at 7pm (his clock status where he forgot to wind up his clock) to his friend house(and as a philosopher he must had calculated how much time it would take to go his friend home in earlier meetings....otherwise he must be a stranger not friend). Let us say the time to travel to his friend house is 10 min, reaches to his friend at 7:10 pm and he stayed night, in the morning he started at 7am to his home from friends house and reaches his home at 7:10 am...Finally he can set his clock 7:10 am.

He walked a straight dessert road. Meaning the angle and length of his shadow was an fairly accurate measurable tool. He looked at his friends clock, then added on the time it took him to walk back to his house, then set his clock for that time.

He could have checked the time that his friend's clock displayed, determined the amount of time that was spent walking from his friend's house to his house (counting the minutes during the journey or a different method), and added the time spent on the journey to his house to the time that was displayed on his friend's clock before he left his friend's house.

May be he knew how much time it takes him to travel to his friend's house.So while leaving from his friend's house he checked his friend's clock and added the travel time along with time hi checked in his friend's clock and wound up the clock accordingly.

The philosopher wound his clock, and set it at 12:00 He walked to his friends house and noted the time he arrived, and compared it to the time he had set, thus determining the time differential between the two clocks. On his return trip he noted the time he left, and when he returned home he adjust his clock for the walking time differential.

Clocks can measure time even when they do not show the right time. You just have to wind the clock up and... We have to suppose that the journey to the friend and back lasts exactly the same time and the friend has a clock (showing the correct time) - it would be too easy if mentioned in the riddle.Suppose he started his journey at the 5PM (but his clock is showing wrong say 3 PM and he dont know it is 5PM) and reached after 2 hrs journey to friends house which shows 7PM and when he returns his clock shows 3+2+2=7 PM so he get to know it took 4 hrs in journey i.e. 2 hrs in half journey. Now he adds 2 to 7 or sets 9 PM in the clock.